A blemish defect in a camera may be manifested by one or more blurred spots as seen when a resulting digital image produced by the camera is displayed. The blurred spots are due to pixels of the digital image that are different from surrounding ones, even though the camera has taken a picture of a calibration-type flat field target that is completely uniform. Blemish defects are typically caused by scratches, staining, or foreign objects (such as dust particles) and may be present on an optical surface within the optical imaging path of the camera. Blemishes may be contrasted with other defects such as vignettes. The latter are usually minor defects that are present in almost every manufactured specimen, and may be alleviated by post-capture image processing that can correct for vignetting and lens shading defects. Blemishes, on the other hand, may be severe enough so as to result in a particular specimen being flagged as a failed unit, during manufacture or production line testing. Image processing-based blemish detection algorithms are available that can be used to screen out units that have or exhibit blemish defects. A goal of such algorithms is to flag only those units that have blemish defects; efforts to improve the accuracy of such algorithms are ongoing, so as to reduce the likelihood of false positives.